FIG. 1 illustrates the basic concept of a pseudowire (PW) in a communication network. In the network 100, pseudowires 105a-b are defined to run over a packet network 115, such as, IP networks, layer two tunneling protocol (L2TP) networks, MPLS networks, etc. These networks provide the packet “cloud” 115 through which connection-oriented tunnels 110 are formed to support pseudowires 105a-b. For the common MPLS case, two unidirectional, inner-tunnel, label-switched paths (LSPs) are contained within unidirectional, outer-tunnel LSPs (which act as traffic-engineering tunnels) and create a bidirectional connection between provider edge (PE) routers.
The inner LSPs form the pseudowires 105a-b by using an interworking function (IWF)—currently residing at the PE, although it can easily and rapidly migrate to the customer equipment (CE)—that encapsulates the CE data transmission format, such as frame relay, asynchronous transfer mode (ATM), or Ethernet, from the attachment circuit into a standard packetized pseudowire format. At the far end of the pseudowire 105a-b, the data is unencapsulated and handed over to the destination CE.